Recently, as exhaustion of existing energy resources such as petroleum and coal is estimated, interests on alternative energies for substituting them are more increased. Among the alternative energies, a solar cell is particularly spotlighted since its energy resource is sufficient and it does not cause any environmental pollution. A solar cell is classified into a solar heat cell that generates a vapor required for rotating a turbine using a solar heat, and a solar light cell that converts photons into electric energy using the properties of a semiconductor. Generally, a solar cell calls the solar light cell (hereinafter, the term ‘solar cell’ is used).
Referring to FIG. 1 showing a basic structure of a solar cell, the solar cell has a junction structure of a p-type semiconductor 101 and a n-type semiconductor 102 like a diode. If photons are input to the solar cell, the photons are reacted with materials of the semiconductor to generate electrons of (−) charge and holes of (+) charge caused by removal of the electrons, thereby allowing flow of electric current as they are moving. It is called photovoltaic effect. Among the p-type semiconductor 101 and the n-type semiconductor 102 that composes the solar cell, electrons are drawn toward the n-type semiconductor 102 and the holes are drawn toward the p-type semiconductor 101, so they are moved to electrodes 103, 104 joined to the n-type semiconductor 101 and the p-type semiconductor 102, respectively. If the electrodes 103, 104 are connected using a cable, it is possible to obtain an electric power as electricity flows.
In addition to the above basic structure of a solar cell, an anti-reflection layer and a reflection layer are respectively provided to front and rear sides of the solar cell in order to enhance the efficiency of the solar cell. The anti-reflection layer and the reflection layer respectively prevent reflection of solar rays inputting onto the front side and also reflect solar rays passing through the rear side of the solar cell, thereby enhancing optical trapping.
The reflection layer should have a high reflectivity for solar rays and also ensure low recombination of carriers on an interface between the reflector layer and a semi-conductor layer. However, a conventional reflection layer does not have excellent reflectivity and sufficient prevention of recombination of carriers. In addition, due to bad thermal stability, the conventional reflection layer has a limit in increasing a temperature of a thermal treatment process used for forming a rear electrode.